Brain Stem and cortical control of motor function

Dr Z Akbari

BS nuclear groups give rise to descending motor tracts that influence motor neurons and their associated interneurons

(posture, locomotion, and eye movements)

Red nucleus (magnocellular part) Vestibular nuclear complex Reticular formation Tectum

Brain stem control of movement

Dr Z Akbari

A. Medial pathways: Main pathways for maintaining posture & head position during movemDescend in the ventral column. Terminate in the ventromedial spinal gray

matter. Pontine(+) and medullary(-) reticulospinal pathway. Lat. VS tract Med.VS tract Tectospinal tracts

B. Lateral pathway : Important for the production of movement, especially in the distal limbs Rubrospinal tract (magnocellular portion of the red n). Descends in the contralateral dorsolateral column. Terminates in the dorsolateral area

of the spinal gray matter.

Medial and lateral descending pathways from the brain stem

Dr Z Akbari

Dr Z Akbari

Cortical motor function

Dr Z Akbari

The motor cortex and corticospinal tract

Primary Motor cortex (4)

Premotor control area (6)

Supplementary motor area

Dr. Z akbari

Control of voluntary movement

• Primary motor cortexControl simple feature of movement

Activity of cortical neurons signals direction and amplitude of muscle force required to produce movement rather than actual displacement of joint*

• Premotor control areaControls complex movement involve multiple joint (reaching &

grasping)Receive fiber from area 5 & 7 ….send to M1Mental rehearsal of movementMovement triggered by external event involved PMv

• Supplementary motor areaCoordinates bilateral movements. Movement triggered internally involved SMAPrepare movement sequences in the absence of visual cuesDr. Z akbari

Population activity in the motor cortex

Dr. Z akbari

Black lines are individual cell vectors. When all of them are summed for a particular direction of movement, the resulting population vector (red)points in essentially the direction of the upcoming movement.

Some specialized area of motor cortex Boca's area

Voluntary eye movement field

Head rotation area

Area for hand skill

Dr. Z akbari

Somatotopic organization of primary motor cortex

Plasticity: change of motor maps with experience

Dr. Z akbari

Corticospinal tract (Pyramidal system)

Corticospinal tract: lat & ventral

Primary MA: 30%

Premotor &SMA: 30%

Somatosensory area: 40%

Giant pyramidal cells (Betz cell)

Extrapyramidal system:Descending BS & spinal pathways that do not pass through pyramid.

-Postural control

The cortex directly controls motor neurons in the SC and BS through descending pathways:

A. The vent. corticospinal tract : o Premotor area (6) and a zones in area 4 controlling the neck and trunk. o The descending fibers terminate bilaterallyo Send collaterals to the medial pathways from the BS.

B. The lat. corticospinal tract:oTwo motor areas (4 & 6) and three sensory areas (3, 2, & 1). oIt crosses at the pyramidal decussation,oThe fibers from the sensory cortex terminate primarily in the medial portion of the dorsal horn. Collateral fibers project to dorsal column nuclei. (allow the brain to actively modify sensory signals).

C. The corticobulbar tract :Lat: ends contralaterally in the part of the facial nucleus that supplies muscles of the lower face and in the hypoglossal nucleus. Med :The remainder of the corticobulbar tract ends bilaterally.

Dr. Z akbari

Dr. Z akbari

Other pathways from the motor cortex Betz cell collateral

Fibers to basal ganglia

Fibers to red nucleus

Fibers to BS: vestibular nuclei and reticular substance

Fibers to pontine nuclei: corticopontocerebellar fiber

Fibers to olivary nucleus……cerebellum

Corticobulbar pathway

Incoming pathways to the motor cortex From other cortical area (Parietal, frontal, occipital, temporal)

From opposite cerebral hemisphere

Somatosensory fiber

Tract from VL & VA n of thalamus ( from basal ganglia & cerebellum)

Fiber from intralaminar nuclei of thalamus: general excitability Dr. Z akbari

Dr. Z akbari

Descending motor pathways

Lateral system:

Lat CS tract

Rubrospinal tract

Concerned with goal directed movemnet

Medial system:

Ventral CS

Reticulospinal

Med & Lat Vestibulospinal

Tectospinal

Provide basic postural control systemDr. Z akbari

Dr Z Akbari